Direct-pressure type mold clamping mechanism

ABSTRACT

A motor-operated, direct-pressure type mold clamping apparatus is capable of high-speed mold closing and opening operations and of producing a required mold clamping force, without the use of a large-sized motor. In the mold opening and closing operations, a ball screw, in engagement with a ball nut which is movable in one with a moving platen, is rotated at high speed by a motor through gears and a clutch, so that a die is opened and closed at high speed. In a mold clamping operation, the ball screw is driven with a large rotatory force transmitted through a clutch and gears which, having a high reduction ratio, serve to increase the rotatory force of the motor. Thus, dies are clamped with a large clamping force.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor-operated, direct-pressure typemold clamping mechanism of an injection-molding machine.

2. Description of the Related Art

An injection-molding machine is furnished with a toggle type moldclamping mechanism, in which a drive source and a moving platen areconnected by means of a toggle link, or a direct-pressure type moldclamping mechanism, in which the drive source and the moving platen areconnected directly. The clamping mechanism serves to open or close andclamp dies that are attached individually to the moving platen and astationary platen.

In the mold clamping operation, the dies must be clamped with a strongforce. Thus, a requisite for the drive source of a mold clampingmechanism is to be capable of producing a strong clamping force. In theprocess of injection molding, moreover, the time required for themanufacture of each molding, i.e, the cycle time, is relatively short.Another requisite for the drive source, therefore, is to be able todrive the dies at high speed while they are being opened or closed.

The toggle link acts to help the dies open or close at high speed, andto facilitate the production of a strong clamping force. Thus, thetoggle type mold clamping mechanism fulfills both of the aforesaidrequirements. The direct-pressure type mold clamping mechanism, on theother hand, has the advantage over the toggle type mold clampingmechanism in that the former does not require mold thickness adjustmentfor compensating the change of the die thickness. It is difficult forthe direct-pressure type mold clamping mechanism, however, to satisfyboth the aforementioned requirements. In the case of a direct-pressuretype mold clamping mechanism using a motor as its drive source, forexample, both of the aforementioned requirements can be fulfilled onlyif the motor used has a very large capacity, since large capacity motorare expensive, the manufacturing cost of the injection-molding machineincreases.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide amotor-operated, direct-pressure type mold clamping mechanism, capable ofhigh-speed mold closing and opening operations and of producing arequired mold clamping force, without the use of a special,large-capacity motor.

In order to achieve the above object, a direct-pressure type moldclamping mechanism according to the present invention comprisesconversion means including a rotating member and a rectilinear motionmember movable in unison with a moving platen, the conversion meansserving to convert a rotary motion of the rotating member into arectilinear motion of the rectilinear motion member; a motor for drivingthe rotating member of the conversion means; transmission means fortransmitting the rotation of the motor to the rotating member, therebyrotating the rotating member at high speed; a speed reducer for reducingand enhancing the rotation speed and the rotatory force of the motor,respectively, and transmitting the rotatory force of the motor, thusenhanced, to the rotating member; and switching means for connecting themotor and the rotating member alternatively by means of the transmissionmeans and the speed reducer.

According to the present invention, as described above, the movingplaten is driven by means of the motor with the aid of the transmissionmeans in a mold closing or opening step, which, although nevernecessitating production of a particularly strong driving force,requires the moving platen to move quickly. In a mold clamping stepwhich, although requiring only low speed and small displacement, demandsproduction of a strong clamping force, on the other hand, mold clampingoperation is performed with use of a motor output enhanced by means ofthe speed reducer. Thus, the mold clamping can be effected without usinga large-capacity motor, and the mold closing and opening operations canbe accomplished in a short time. Accordingly, an economicalinjection-molding machine with a shorter required cycle time isobtained.

Moreover, the maximum output torque of the motor used need not be great.By limiting the torque of the motor output, dies are protected due tothe small, optimum die protection force utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view substantially showing the a direct-pressuretype mold clamping apparatus according to a first preferred embodimentof the present invention; and

FIG. 2 is a schematic view showing an apparatus according to a secondpreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a direct-pressure type mold clamping mechanism according toa preferred embodiment of the present invention. In FIG. 1, numerals 1and 2 denote a moving platen and a stationary platen, respectively.These platens 1 and 2 are fitted with dies 3 and 4, respectively. Thestationary platen 2 is fixed to a base 21 of an injection-moldingmachine, and the moving platen 1 can slide from side to side, as in FIG.1, along a tie bar (not shown) extending between a rear platen (notshown), which is fixed to the base 21 of the injection-molding machine,and the stationary platen 2. Numeral 5 denotes a nut fixing base whichis fixed to the moving platen 1 by means of bolts or the like. A nutmounting plate 6 is fixed to one end of the nut fixing base 5 by meansof bolts or the like. Further, a ball nut 7 is fixed to the nut mountingplate 6 by means of bolts or the like. Elements 1 and 5 to 7 constitutean integral structure.

A ball screw 8, which mates with ball nut 7, is mounted so that its axisis substantially in alignment with the center of the moving platen 1.Namely, the ball screw 8 is positioned so that the dies 3 and 4 can beclamped evenly when the moving platen 1 is moved, through the medium ofthe ball nut 7, the nut mounting plate 6, and the nut fixing base 5.Axial movement of moving platen is effected by rotating the ball screw8.

A ball screw shaft 8a, which is integral with the ball screw 8, has oneend rotatably supported at the base 21 (or a rear platen fixed thereto)of the injection-molding machine by means of a thrust bearing 20. Gears9 and 13 are fixed to the ball screw shaft 8a, and a gear 10 meshes withthe gear 9. The gear 10 is releasably coupled to a driving shaft 12 bymeans of an electromagnetic clutch 11. Moreover, the gear 13 meshes withan idler 14, which is in with a gear 15. The gear 15 is also releasablycoupled to the driving shaft 12 by means of an electromagnetic clutch16. The driving shaft 12 is connected to a motor 17. A braking system 19is mounted on a shaft to which is connected a gear 18 meshing with thegear 9. The motor 17 and the braking system 19 are fixed to the base 21of the injection-molding machine, and the idler 14 is supported by thebase 21, although junctions between them are not illustrated.

In the present embodiment, the gears 9 and 10 constitute a speedreducer, which serves to reduce the rotation speed of the driving shaft12 and transmit increased torque to the ball screw shaft 8a. On theother hand, the gear 13, the idler 14, and the gear 15 constitutetransmission means for transmitting the rotation of the driving shaft 12to the ball screw shaft 8a with a rotating speed ratio of 1:1.

In FIG. 1, numeral 100 denotes a device for controlling the drive of theclutches 11 and 16, the motor 17, and the braking system 19. Adescription of the device 100 is omitted herein, since this device canbe constructed by a conventional technique.

A mold clamping apparatus according to the present embodiment will nowbe described.

First, in closing the dies 3 and 4, the clutch 11 is disengaged todisconnect the driving shaft 12 and the gear 10, while the clutch 16 isengaged to connect the driving shaft 12 and the gear 15. At the sametime, the braking system 19 is released. When the motor 17 is rotated inthe mold closing direction, the ball screw 8 is rotated at high speed bymoment transmitted through the driving shaft 12, clutch 16, gear 15,idler 14, gear 13, and ball screw shaft 8a. Thereupon, the ball nut 7 inengagement with the ball screw 8 advances, thereby moving the die 3 inthe mold closing direction (from right to left of FIG. 1), the die 3being mounted on the moving platen 1 which is integral with the nutmounting plate 6 and the nut fixing base 5. When the die 3 reaches a dieprotection start position, the rotating speed of the motor 17 is reducedso that the die 3 is driven at a die protection speed.

When the die 3 reaches the position where it touches the die 4, theclutch 16 is disengaged to disconnect the driving shaft 12 and the gear15, and the braking system 19 is actuated to lock and prevent the ballscrew 8 from rotating further. Then, the clutch 11 is engaged to connectthe driving shaft 12 and the gear 10, and the braking system 19 isreleased. By doing this, the rotation speed of the motor 17 istransmitted in a reduced mode to the ball screw shaft 8a, through thedriving shaft 22, clutch 11, gear 10, and gear 9, so that the ball screw8 is rotated at low speed. As the ball screw 8 rotates, the die 3 movesin the mold closing direction, as mentioned before, so that the dies 3and 4 are clamped together. In doing this, the rotating speed and therotatory force of the motor 17 are reduced and enhanced, respectively,by means of the gears 10 and 9, as a result, strong mold clamping forceis produced. When a suitable sensor 3a detects an arrival of the die 3aat position which produces a set clamping force is, the braking system19 is worked, the clutch 11 is disengaged, and the drive of the motor 17is stopped.

When starting mold opening after the end of injection, hold or the like,the braking system 19 is released, the clutch 16 is engaged, and themotor 17 is rotated in a mold opening direction (reversely) at a moldrelease speed. Thus, the ball screw 8 is rotated reversely to therotation for the mold closing through the medium of the clutch 16,driving shaft 12, gear 15, idler 14, gear 13, and ball screw shaft 8a.After the die 3 reaches an acceleration position, the rotation of themotor 17 is accelerated. When the die 3 then reaches a decelerationposition, the speed of the motor 17 is reduced. When the die 3 reaches amold opening end position, the motor 17 is stopped. Thus, one cycle ofoperation, including the steps of mold closing, mold clamping, and moldopening, is finished.

In the embodiment described above, the braking system 19 is designed soas to be able to lock the gear 18 in mesh with the gear 9.Alternatively, however, the brake system 19 may directly lock the ballscrew shaft 8. Further, the clutch 11 need not always be located betweenthe driving shaft 12 and the gear 10. For example, an alternativeclutch, which replaces the clutch 11, may be provided between the gears15 and 10 on the driving shaft 12, in a manner such that the gear 10 isfixed directly on one side of the driving shaft 12. Alternatively,instead of clutch 16, a clutch may be provided between the ball screwshaft 8a and the gear 13. In this case, the gear 15 is fixed directly onthe driving shaft 12.

Moreover, the motor 17 may be formed of a servomotor. In this case, thebrake 19 need not always be used, since the servomotor operates so as tohold the die 3 in position while switching from mold closing to moldclamping or during the mold clamping step.

FIG. 2 shows a direct-pressure type mold clamping mechanism according toa second preferred embodiment of the present invention. In thedescription to follow, like reference numerals are used to designate thesame members as are used in the first embodiment. More specifically,numeral 1 denotes a moving platen; 2, a stationary platen; 3 and 4,dies; and 5, a nut fixing base fixed to the moving platen 1.

This embodiment differs from the first embodiment, which uses the ballnut 7 and the ball screw 8 forming a pair, mainly in that two pairs ofball nuts and ball screws for coarse and fine adjustment are usedinstead. A nut mounting plate 30 is fixed to the nut fixing base 5 bymeans of bolts or the like, and a fine-adjustment ball screw 32 is inengagement with a fine-adjustment ball nut 31 which is fixed to the nutmounting plate 30. The nut mounting plate 30 can slide along a guidesurface 35 of a coarse-adjustment feed table 34, in a direction (fromside to side as in FIG. 2) such that the dies 3 and 4 are opened orclosed. A ball nut 37 for coarse adjustment is fixed to thecoarse-adjustment feed table 34, and a ball screw 38 for coarseadjustment is in engagement with the ball nut 37. As thecoarse-adjustment ball screw 38 rotates, the coarse-adjustment ball nut37 and the coarse-adjustment feed table 34 move in the opening orclosing direction for the dies 3 and 4. The coarse-adjustment feed table34 is guided by a guide rod (not shown) or the like so as to be movablein the opening or closing direction for the dies 3 and 4. A brakingsystem 40 is fixed to the base of the injection-molding machine, wherebya ball screw shaft 39, which is integral with the coarse-adjustment ballscrew 38, is prevented from rotating. One end of the ball screw shaft 39is separably coupled to a shaft 43 of a gear 42 by means of anelectromagnetic clutch 41. The gear 42 meshes with a gear 45 which isdriven by means of a motor 44.

A bearing plate 36 is fixed integrally on the coarse-adjustment table34. A ball screw shaft 33, which is integral with the fine-adjustmentball screw 32, extends through the bearing plate 36, and is supported bymeans of a thrust bearing 46 which is attached to the bearing plate 36.One end of the ball screw shaft 33 is separably coupled to a splineshaft 49 by means of a clutch 48. A braking system 47, which is fixed tothe bearing plate 36, is provided in operative relation with the ballscrew shaft 33. A gear 50 is spline-coupled to the spline shaft 49. Thegear 50 meshes with the gear 45 which is driven by the motor 44. Thereduction ratio between the gears 45 and 50 is set to a larger value,and the gears 45 and 50 constitute a speed reducer. On the other hand,the gears 45 and 42 constitute transmission means with a rotationalratio of 1:1.

The operation of the mold clamping mechanism according to this secondembodiment will now be described.

First, in the mold closing operation, the clutches 48 and 41 aredisengaged and engaged, respectively, by means of the drive controldevice 100. Then, the braking system 47 is worked to lock the rotationof the fine-adjustment ball screw 32, while the braking system 40 isreleased. Subsequently, the motor 44 is driven in the mold closingdirection, so that the ball screw shaft 39 and the coarse-adjustmentball screw 38 integral therewith are rotated at high speed through themedium of the gears 45 and 42 and the clutch 41. In the meantime, thefine-adjustment ball screw 32 is released from the spline shaft 49 bydisengagement of the clutch 48, at the same time the ball screw islocked and prevented from rotating by the actuating braking system 47.

As the coarse-adjustment ball screw 38 rotates, the coarse-adjustmentfeed table 34, which is integral with the ball nut 37 in engagement withthe ball screw 38, moves in the mold closing direction. Also, the ballscrew shaft 33 and the fine-adjustment ball screw 32, which are enabledto move in unison with the feed table 34 by means of the bearing plate36 and the braking system 47, move in the same direction. At the sametime, the die, mounted on the moving platen 1 which is connected to anut fixing base 5 and is movable with the nut mounting plate 30, movesat high speed in the mold closing direction. Then the spline shaft 49and the clutch 48, along with the coarse-adjustment feed table 34, alsomove from right to left of FIG. 2.

When the die 3 reaches the die protection start position, the rotatingspeed of the motor 44 is lowered to the die protection speed. When thedie 3 touches the die 4, the braking system 40 is actuated to lock therotation of the coarse-adjustment ball screw 38, the clutches 41 and 48are disengaged and engaged, respectively, and the braking system 47 isreleased. Thereupon, the rotation speed of the motor 44 is reduced bythe speed reducer which is composed of the gears 45 and 50. Torque istransmitted to the fine-adjustment ball screw 32 through the splineshaft 49, the clutch 48, and the ball screw shaft 33, thereby causingthe ball screw 32 to rotate. As the ball screw 32 rotates, the die 3moves in the mold closing direction, urged by the nut mounting plate 30,the nut fixing base 5, and the moving platen 1, the plate 30 beingintegral with the ball nut 31 and slidable relatively to thecoarse-adjustment feed table 34. Thus, dies 3 and 4 are clampedtogether. In this case, the rotatory force or torque of the motor 44 isenhanced by the speed reducer composed of the gears 45 and 50. Thus alarger clamping force is produced, whereby the clamps 3 and 4 areclamped fast. When the die 3 reaches the position where the set clampingforce is produced, the braking system 47 is actuated to lock therotation of the fine-and coarse-adjustment ball screws 32 and 38, thedrive of the motor 44 is stopped, and the clutch 48 is disengaged.

Subsequently, in the mold opening operation, the braking systems 47 and40 are first actuated and released, respectively, and the clutches 41and 48 are engaged and disengaged, respectively. Then, the motor 44 isrotated in the mold opening direction, the coarse-adjustment ball screw38 is rotated at the mold release speed, and the die 3 is moved in themold opening direction. When the die 3 reaches an acceleration startposition, the rotation of the motor 44 is accelerated. When the die 3reaches a deceleration start position, the motor 44 is then decelerated.The coarse-adjustment feed table 34 reaches a position corresponding toa mold closing start position for the die 3, the braking system 40 isactuated, the clutch 41 is disengaged, the braking system 47 isreleased, and the clutch 48 is engaged. Thereupon, the fine-adjustmentball screw 32 rotates, so that the nut mounting plate 30 is drivenrelatively to the coarse-adjustment feed table 34 in the mold openingdirection until the plate 30 reaches its mold clamping start position.Thus, the die 3 reaches the mold opening end position.

In the mold opening operation, the sequence of operation may be changedas follows. The nut mounting plate 30 is first returned to its moldclamping start position on the coarse-adjustment feed table 34,whereupon the coarse-adjustment feed table 34 is returned to itsposition corresponding to the mold opening end position.

When using a motor of any type other than a servomotor for the motor 44,the motor 44 must be controlled by detecting the respective positions ofthe coarse-adjustment feed table 34 and the nut mounting plate 30 bymeans of various sensors. When using a servomotor for the motor 44, onthe other hand, the sensors need not be provided, this is because thedisplacement of the coarse-adjustment feed table 34 and that of the nutmounting plate 30 relative to the coarse-adjustment feed table 34 can bedetected by means of a position detector attached to the servomotor.

According to the present invention, as described in connection with thefirst and second embodiments, the mold closing and opening speeds areincreased, and a strong clamping force can be produced, without usingany large-capacity motor. Since the motor used is not particularly largein capacity, a torque limit operation for limiting the output torque ofthe motor can be effected for die protection during the mold closingoperation. More specifically, if a large-capacity motor with the maximumoutput torque of e.g., 100 tons is subjected to torque limit, the outputtorque obtained at the time of die protection is 1 ton at the minimum,since the torque limit resolving power is about 1/100. According to thepresent invention, however, the transmission means and the speed reducerare used alternatively, and transmission of the output torque of themotor to the moving platen traces power path for the mold opening andclosing operations and another for the mold clamping operation. Thus,according to the invention, a general-purpose motor with the maximumoutput of about 2 or 3 tons may be used. If such a motor is subjected totorque limit, its output torque can be lowered to about 20 kg to 30 kg,so that an optimum die protection pressure can be obtained.

We claim:
 1. A direct-pressure mold clamping apparatus for aninjection-molding machine having a moving platen, comprising:conversionmeans including a rotating member and a rectilinear motion membermovable in unison with the moving platen, said conversion means forconverting rotary motion of said rotating member into rectilinear motionof said rectilinear motion member; a feed table movably supporting saidmoving platen; a motor having a drive shaft for driving the rotatingmember of said conversion means; a transmission coupled to the motor; afirst ball screw/nut mechanism for course-adjustment having acourse-adjustment nut coupled to said feed table and a course-adjustmentball screw driven by said motor through said transmission for moving themoving platen under a relatively high speed, low torque condition; asecond ball screw/nut mechanism for fine adjustment having afine-adjustment nut fixedly coupled to said moving platen and afine-adjustment ball screw spline-coupled to a speed reducer and beingdriven by said motor for moving the moving platen under a relatively lowspeed, high torque condition; said transmission transmitting therotation of said motor drive shaft to said course-adjustment ball screw;said speed reducer for reducing the rotational speed of saidfine-adjustment ball screw while increasing the rotary force of saidmotor, and transmitting the rotary force of said motor to saidfine-adjustment ball screw; and switching means for alternativelyconnecting said motor to said fine-adjustment ball screw and saidcourse-adjustment ball screw through said transmission and said speedreducer, respectively.
 2. A direct-pressure mold clamping apparatusaccording to claim 1, further comprising braking means for locking saidrotating member.
 3. A direct-pressure mold clamping apparatus accordingto claim 1 further comprising a sensor for detecting the position of themoving platen, and a control device for controlling said motor based onthe position detected by the sensor, wherein said motor is a servomotor.4. A direct-pressure mold clamping apparatus according to claim 1,wherein said switching means includes a first clutch for connecting anddisconnecting said course-adjustment ball screw from the motor shaft,braking means for locking the rotation of said course-adjustment ballscrew, a second clutch for connecting and disconnecting saidfine-adjustment ball screw from the motor shaft, and braking means forlocking the rotation of said fine-adjustment ball screw, saidfine-adjustment nut being axially slidable with respect to saidcoarse-adjustment nut and movable in unison with said moving platen. 5.A mold clamping apparatus having a movable die fixed to a movable platenand a stationary platen, the apparatus comprising:a motor having arotary power output shaft; a feed table movably supporting the movableplaten; a first ball nut supported on the feed table; a first ball screwthreadedly engaging the first ball nut and having a rotatably supportedintegrally formed shaft driven by the motor to move the movable platenand the feed table in unison under a relatively high speed, low torquecondition; a second ball nut fixedly connected to the movable platen; asecond ball screw threadedly engaging the ball nut and having arotatably supported integrally formed shaft driven by the motor formoving the movable platen relative to the feed table under a relativelylow speed, high torque condition; a transmission for transmitting powerfrom the motor shaft to the first ball screw shaft; a speed reducer fortransmitting power from the motor shaft to the second ball screw shaftat a reduced rotational speed and increased torque; and switching meansfor alternatively connecting the transmission and the speed reducer tothe motor shaft.
 6. A mold clamping apparatus according to claim 5,wherein the transmission comprises a first gear connected to the motorshaft, a second gear meshing with the first gear and having a shaftdetachably connected to the first ball screw shaft.
 7. A mold clampingapparatus according to claim 6, wherein the speed reducer comprises aspeed reducer gear meshing with the first gear, a splined shaftdetachably connected to the second ball screw shaft and supporting thespeed reducer gear and being axially movable relative to the speedreducer gear.
 8. A mold clamping apparatus according to claim 7, whereinthe switching means comprises:a first clutch between the first ballscrew shaft and the second gear shaft, and a second clutch between thesecond ball screw shaft and the splined shaft, and a controller foralternatively outputting switching signals to the first and secondclutches.